title: Adaptive plan selection vs. re-optimisation in radiotherapy for bladder cancer: a dose accumulation comparison.
abstract: OBJECTIVE
  Patients with urinary bladder cancer are obvious candidates for adaptive radiotherapy (ART) due to large inter-fractional variation in bladder volumes. In this study we have compared the normal tissue sparing potential of two ART strategies: daily plan selection (PlanSelect) and daily plan re-optimisation (ReOpt).
  
  
  METHODS
  Seven patients with bladder cancer were included in the study. For the PlanSelect strategy, a patient-specific library of three plans was generated, and the most suitable plan based on the pre-treatment cone beam CT (CBCT) was selected. For the daily ReOpt strategy, plans were re-optimised based on the CBCT from each daily fraction. Bladder contours were propagated to the CBCT scan using deformable image registration (DIR). Accumulated dose distributions for the ART strategies as well as the non-adaptive RT were calculated.
  
  
  RESULTS
  A considerable sparing of normal tissue was achieved with both ART approaches, with ReOpt being the superior technique. Compared to non-adaptive RT, the volume receiving more than 57 Gy (corresponding to 95% of the prescribed dose) was reduced to 66% (range 48-100%) for PlanSelect and to 41% (range 33-50%) for ReOpt.
  
  
  CONCLUSIONS
  This study demonstrated a considerable normal tissue sparing potential of ART for bladder irradiation, with clearly superior results by daily adaptive re-optimisation.
authors.affiliation: Department of Medical Physics, Aarhus University Hospital, Aarhus C, Denmark. Electronic address: annveste@rm.dk.
authors.forename: Anne
authors.initials: A
authors.lastname: Vestergaard
authors.forename: Ludvig Paul
authors.initials: LP
authors.lastname: Muren
authors.forename: Jimmi
authors.initials: J
authors.lastname: Søndergaard
authors.forename: Ulrik Vindelev
authors.initials: UV
authors.lastname: Elstrøm
authors.forename: Morten
authors.initials: M
authors.lastname: Høyer
authors.forename: Jørgen B
authors.initials: JB
authors.lastname: Petersen
mesh_terms: D054893:Cone-Beam Computed Tomography / Q000379:methods; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D008297:Male; D009367:Neoplasm Staging; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D001749:Urinary Bladder Neoplasms / Q000473:pathology / Q000532:radiotherapy*
keywords: Adaptive radiotheraphy; Bladder cancer; Dose accumulation; Plan-of-the-day; Re-optimisation